Coated metal strip

ABSTRACT

A corrosion-resistant colored architectural material which is essentially lead free and is not highly reflective. The coating on the material is a two-phase metallic coating comprised of a large weight percentage of zinc and a relatively large weight percentage of tin. The tin-zinc composition provides for both a highly corrosive-resistant coating which protects the surface of the architectural material from oxidation and also produces a gray, earth tone colored which is not highly reflective.

This patent application is a continuation of patent application Ser. No.175,523, filed Dec. 30, 1993 and issued to U.S. Pat. No. 5,401,586 onMar. 28, 1995 which is in turn a continuation-in-part of abandonedpatent application Ser. No. 154,376, filed Nov. 17, 1993, which is inturn a continuation of abandoned patent application Ser. No. 042,649,filed Apr. 5, 1993.

The present invention relates to the art of metal architecturalmaterials and more particularly to an architectural sheet material thatis environmentally friendly while providing long life and desiredcolorization.

Incorporation By Reference

As background material, so that the specification need not specify indetail what is known in the art, Assignees' U.S. Pat. Nos. 4,987,716 and4,934,120 illustrate metal roofing systems of the type to which thisinvention can be used and are incorporated herein by reference. U.S.patent application Ser. No. 000,101 filed Jan. 4, 1993, illustrating aprocess of hot-dip coating roofing materials, is also incorporatedherein by reference.

BACKGROUND OF THE INVENTION

Over the years, architectural materials, such as metal roofing systemsand metal siding systems, made of pliable metals in various sheet gaugethicknesses have been used. Metals such as carbon steel, stainlesssteel, copper and aluminum are the most popular types of metal. Thesearchitectural metal materials are commonly treated withcorrosion-resistant coatings to prevent rapid oxidation of the metalsurface, thereby extending the life of the materials. A popularcorrosion-resistant coating for carbon steel and stainless steel is aterne coating. Terne coating has been the predominate and most popularcoating for roofing materials due to its relatively low cost, ease ofapplication, excellent corrosion-resistant properties and desirablecolorization during weathering. The terne coating is an alloy typicallycontaining about 80% lead and the remainder tin. The coating isgenerally applied to the architectural materials by a hot-dip processwherein the material is immersed into a molten bath of terne metal.Although terne coated sheet metals have exhibited excellent resistantproperties and have been used in a variety of applications, the ternecoating has been questioned in relation to its impact on theenvironment. Environmental and public safety laws have been recentlyproposed and/or passed prohibiting the use of materials containing lead.Because the terne alloy contains a very high percentage of lead,materials coated with terne have been prohibited in various types ofusages or applications such as aquifer roofing systems. The concern oflead possibly leaching from the terne coating has made such coatedmaterials inadequate and/or undesirable for several types of buildingapplications. The terne alloy has a further disadvantage in that thenewly applied terne is very shiny and highly reflective. As a result,the highly-reflective coating cannot be used on buildings or roofingsystems such as at airports and military establishments. The ternecoating eventually loses its highly-reflective properties as thecomponents within the terne coating are reduced (weathered); however,the desired amount of reduction takes approximately 11/2 to 2 years whenthe terne coating is exposed to the atmosphere, thus requiring the ternemetals to be stored over long periods of time prior to being used inthese special areas. The storage time is significantly prolonged if theterne-coated materials are stored in rolls and the rolls are protectedfrom the atmosphere.

Tin coating of carbon steel is a well-known process for use in the foodindustry. However, in the specialized art of architectural materials, atin coating for architectural materials has not been used until done bythe present inventors. The most popular process for applying a tincoating to carbon steel for use in the food industry is by anelectrolysis process. In an electrolysis process, the coating thicknessis very thin and typically ranges between 3.8×10⁻⁴ to 20.7×10⁻⁴ mm(1.5×10⁻⁵ to 8.15×10⁻⁵ in.). Furthermore, the equipment and materialsneeded to properly electroplate the metal materials are very expensiveand relatively complex to use. The expense of applying anelectroplated-tin coating and the limited obtainable thicknesses of thetin coating are a disadvantage for using such a process for building androofing materials. A hot-dip process for applying the tin coating may beused; however, if the architectural materials are not properly preparedand the coating is not properly applied to the roofing materials, minuteareas of discontinuity in the tin coating may occur resulting innon-uniform corrosion protection. This is especially a problem when thetin is applied to stainless steel materials by a hot-dip process. Tin isnot electroprotective to steel under oxidizing conditions. Consequently,discontinuities in the tin coating result in the corrosion of theexposed metal. Tin coatings have the further disadvantage of having ahighly-reflective surface. As a result, architectural materials coatedwith a tin coating cannot be used in an environment wherehighly-reflective materials are undesirable until the coated materialsare further treated (i.e. painted) or the tin is allowed time tooxidize.

Coating architectural materials with zinc metal, commonly known asgalvanization, is another popular metal treatment to inhibit corrosion.Zinc is a highly desirable metal to coat architectural materials withbecause of its relatively low cost, ease of application (i.e. hot-dipapplication) and excellent corrosion resistance. Zinc is alsoelectroprotective to steel under oxidizing conditions and prevents theexposed metal, due to discontinuities in the zinc coating, fromcorroding. This electrolytic protection extends away from the zinccoating over exposed metal surfaces for a sufficient distance to protectthe exposed metal at cut edges, scratches, and other coatingdiscontinuities. With all of the advantages of using zinc, zinc coatingshave several disadvantages that make it undesirable for many types ofbuilding applications. Although zinc coatings will bond to many types ofmetals, the formed bond is not strong and can result in the zinc coatingflaking off the building materials. Zinc is also a very rigid andbrittle metal and tends to crack and/or flake off when the buildingmaterials are formed on site, i.e. press fitting of roofing materials.

Due to the various environmental concerns and problems associated withcorrosion-resistant coatings applied to metal architectural materials,there has been a demand for a coating which can be easily andsuccessfully applied to materials that protect the materials fromcorrosion, does not have a highly-reflective surface subsequent toapplication

SUMMARY OF THE INVENTION

The present invention relates to a corrosion-resistant coatingformulation for use on architectural materials wherein the coating isenvironmentally friendly, has a low lead content and quickly weathers toa non highly-reflective desirable surface.

In accordance with the principal feature of the invention, there isprovided an architectural material typically of stainless steel orcarbon steel coated with a tin-zinc alloy. The tin-zinc coating is atwo-phase metal coating comprising a large weight percentage of zinc anda relatively large weight percentage of tin. The tin content of thetwo-phase coating is less than 35 weight percent and the zinc content isat least 65 weight percent. The unique tin-zinc combination provides forboth a corrosion-resistant coating that protects the surface of thearchitectural material from oxidation and also forms a gray surface,which is very similar to weathered terne, and which is also not highlyreflective.

In accordance with another aspect of the present invention, the tin-zinccoating is applied to the metal roofing materials by a hot-dip process.If the tin-zinc coating is to be applied to stainless steelarchitectural materials, the coating is preferably applied to theroofing materials in similar fashion as disclosed in Assignees'application Ser. No. 000,101 filed on Jan. 4, 1993 and incorporatedherein. "Stainless steel" in the application means a large variety ofalloy metals containing chromium and iron. The alloy may also containother elements such as nickel, carbon, molybdenum, silicon, manganese,titanium, boron, copper, aluminum, nitrogen and various other metals orcompounds. Elements such as nickel can be flashed (electroplated) ontothe surface of the chromium-iron alloy or directly incorporated into thechromium-iron alloy. The hot dip process disclosed in Ser. No. 000,101must be slightly modified to accommodate the higher temperaturesnecessary to hot-dip coat the tin-zinc coating. Tin melts at 232° C.(450° F.) and lead melts at 328° C. (622° F.). In the hot dip process ofSer. No. 000,101, the coating metal has a large amount of tin thuscausing the melting temperature of the coating to be close to 232° C.(450° F.). In the present invention, the zinc component of the metalcoating is the largest component. Zinc melts at 420° C. (788° F.). As aresult, the melting point of the tin-zinc coating approaches 420° C.which is a significantly higher temperature than which was used in theprocess disclosed in Ser. No. 000,101. To accommodate for the highertemperatures, the coating vat may have to be made of a material whichcan withstand the higher temperatures. Furthermore, the time for coolingthe tin-zinc coating may have to be increased. Other than thesemodifications, the process disclosed in Ser. No. 000,101 is used to coatthe novel tin-zinc coating onto stainless steel. The hot-dip processdisclosed in Serial No. 000,101 can be used to coat architecturalmaterials made of metals other than stainless steel such as carbonsteel, aluminum, copper, bronze, etc.

In accordance with another aspect of the invention, bismuth and antimonymay be added to the tin-zinc coating to inhibit the crystallization ofthe tin in cold weather. When tin crystallizes, the bonding of thetin-zinc coating to the roofing materials may weaken resulting inflaking of the coating. The addition of small amounts of bismuth and/orantimony prevents such crystallization of the tin. Bismuth or zinc maybe added in larger quantities to also enhance the hardness and strengthof the tin-zinc coating to increase the resistance to wear of thecoating.

In accordance with another feature of the present invention, thetin-zinc coating is essentially lead free. The lead content ismaintained at extremely low levels not exceeding 0.05 weight percent.Preferably, the lead content is maintained at much lower weightpercentage levels so as to dispense with any environmental concernsassociated with the tin-zinc coating.

In accordance with yet another feature of the present invention, thetin-zinc coating composition is such that the coating provides excellentcorrosion resistance and the coated materials can be formed on sitewithout the tin-zinc coating cracking and/or flaking off. The amount ofzinc in the tin-zinc coating is controlled such that the coating doesnot become too rigid and brittle.

In accordance with still another aspect of the present invention, themetallic roofing materials are plated with a nickel barrier prior toapplying the tin-zinc coating to provide additional corrosionresistance, especially against halogens such as chlorine. The nickelbarrier is applied to the metal building materials at a thin layer.Although the tin-zinc coating provides excellent protection against mostf these corrosion-producing elements and compounds, compounds such aschlorine have the ability to eventually penetrate the tin-zinc coatingand attack and oxidize the surface of the metallic building materialsthereby weakening the bond between the roofing material and the tin-zinccoating. The nickel barrier has been found to provide an almostimpenetrable barrier to these elements and/or compounds which in factpenetrate the tin-zinc coating. Due to the very small amount of thesecompounds penetrating the tin-zinc coating, the thickness of the nickelbarrier can be maintained at thin thicknesses while still maintainingthe ability to prevent these components from attacking the metal roofingmaterial. The tin-zinc coating and thin nickel coating effectivelycomplement one another to provide superior corrosion resistance.

The primary object of the present invention is the provision of anarchitectural material coated with a metallic coating which is highlycorrosive resistant.

Another object of the present invention is the provision of anarchitectural material treated with a metallic coating that is nothighly reflective.

Yet another object of the present invention is a metallic coating, asdefined above, which is a two-phase system comprised of tin and zinc.

Yet another object of the present invention is the provision of aroofing material having a tin-zinc metallic coating which is essentiallylead free.

Still yet another object of the present invention is to provide atwo-phase, tin-zinc metallic coating applied to a base metal sheet whichcoated sheet can be formed and sheared to form various building androofing components that can be subsequently assembled on site withoutthe metallic coating flaking off, chipping, and/or cracking.

Still another object of the present invention is the provision ofproviding a tin-zinc coated roofing material which can be preformed intoroof pans and subsequently seamed on site either by pressed seams orsoldered seams into waterproof joints.

Another object of the present invention is the provision of applying athin nickel barrier to the surface of the roofing material prior toapplying the tin-zinc coating.

These and other objects and advantages will become apparent to thoseskilled in the art upon reading of the detailed description of theinvention set forth below.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The tin-zinc coating is a two-phase metallic coating which, when appliedto stainless steel or low carbon steel materials, forms a highlycorrosion-resistant coating that reduces the corrosion of the materialswhen exposed to the atmosphere. The tin-zinc coating contains a largeweight percentage of zinc and essentially the balance of tin. It hasbeen discovered that by adding zinc in the amounts of at least 65 weightpercent of the tin-zinc alloy, the corrosion resistance of the two-phasemetallic coating is significantly increased as compared to a protectivecoating essentially composed of tin. Although the exact reasons for thisphysical phenomenon of increased corrosion resistance due to theaddition of zinc to tin is unknown to the inventors, it has been foundthat by adding zinc to tin, the two-phase metallic coating exhibitscorrosive-resistant properties which exceed that of tin coatings and, insome environments, that of a terne coating. The tin-zinc coating iselectroprotective under oxidizing conditions which inhibits oxidation ofexposed metal near the tin-zinc coating. As a result, minordiscontinuities in the tin-zinc coating do not result in oxidation ofthe exposed metal, a contrary result if only a tin coating is used. Thetin-zinc coating may contain small amounts of other metals to modify thephysical properties of the tin-zinc, two-phase metallic coating;however, these secondary metal components contribute primarily to thestrength of the coating and not to the corrosion-resistant properties ofthe coating. The tin-zinc coating can be applied to both stainless steeland carbon steel materials by preferably using a conventionalhot-dipping process; however, the coating may be applied by other meanssuch as by electroplating, an airknife process, etc. The tin-zinccoating is not limited to only the protection of stainless steel andcarbon steel and may also be applied to other metals such as copper,bronze, tin, titanium, etc.

The large zinc content of the two-phase metallic tin-zinc coating hasnot been previously used, especially on architectural materials such asmetallic building and roofing materials. The bonding of the tin-zinccoating to carbon steel and stainless steel roofing materials issurprisingly strong and forms a durable protective coating which is noteasily removable, thereby resisting flaking of the coating. The surfacesof the metallic roofing and building materials may be pretreated priorto the coating to improve the bonding between the tin-zinc coating andthe surface of the metallic roofing material. For stainless steelmaterials, pickling the surface of the stainless steel provides forsignificantly greater bonding of the coating. Preferably, the picklingprocess disclosed in Assignees' application Ser. No. 000,101 is used tomaximize the bonding of the tin-zinc coating to the stainless steelmaterials.

The life of the architectural material is significantly extended bycoating the material with the tin-zinc metallic coating. The tin-zinccoating acts as a barrier to the atmosphere which prevents the metalliccoating from oxidizing and/or reducing in the presence of oxygen, carbondioxide or other reducing agents in the environment. Although thetin-zinc coating oxidizes in the presence of various reducing agents inthe atmosphere, the rate of oxidation is significantly slower than thatof the architectural materials. Furthermore, the tin and zinc oxidewhich forms on the coating surface provides corrosion resistance to thetin-zinc coating itself which further enhances the corrosion protectionprovided by the tin-zinc coating. The tin-zinc oxides also reduce thereflectivity of the tin-zinc coating and color the tin-zinc coating.Terne coated materials have become very popular since terne coatedmaterials eventually weather and turn a grey, earth tone color. Theinventors discovered that the novel tin-zinc formulations forms acolored coating which closely matches the popular grey, earth tone colorof weathered terne. Furthermore, by coating the building materials withthe tin-zinc coating, the usable life of the materials is extendedtypically beyond the life of the structure the coated materials are usedon due to the corrosion-resistance of the tin-zinc coating.

The tin-zinc coating is primarily composed of tin and zinc and containslittle, if any, lead thus making the coating essentially lead free andenvironmentally friendly. The lead content, if any, is maintained atextremely low levels within the metallic coating. The amount of lead inthe tin-zinc coating is maintained such that no more than 0.05 weightpercent is present in the coating. Preferably, the lead content in thecoating is maintained at levels less than 0.01 weight percent. Thelimiting of lead content in the metallic coating eliminates any concernsassociated with the leaching of the lead from the metallic coating andthe environmental concerns associated with products containing lead.

The tin-zinc metallic coating is a two-phase system which contains alarge weight percentage of zinc. Preferably, the zinc weight percentageis at least 65% and can be as much as 85% of the tin-zinc coating. Thetin content within the metallic coating essentially makes up the balanceof the metallic coating. The zinc content ranges between 15-35 weightpercent of the tin-zinc metallic coating. Preferably, the metalliccoating includes 20 weight percent tin. The tin-zinc system forms atwo-phase metallic coating. A two-phase system is defined as a metalalloy comprising two primary components. Surprisingly, the inventorshave found that the tin-zinc coating provides a protective coating witha higher corrosion resistance as compared to a tin coating primarilymade up of tin. The amount of zinc within the metallic coating ismaintained so as not to exceed 85% so that the metallic coating remainsrelatively pliable for use in a press-fit roofing system. The inventorshave discovered that the use of large weight percentages of zinc in thetin-zinc alloy does not cause the coating to be too rigid or brittlethus preventing the coated material to be formed or bent which resultsin a cracked coating. In application Ser. No. 042,649, the inventors,when first developing the novel tin-zinc coating, believed that zincweight percentages above 30 weight percent would make the coating rigidand brittle which would result in the cracking of the tin-zinc coatingwhen the coated material was bent or formed. Shortly after the filing ofapplication Ser. No. 042,649, extensive experimentation was performed ontin-zinc coatings having a zinc content above 50 weight percent.Surprisingly, the inventors discovered that a tin-zinc coatingcontaining 65-85 weight percent zinc and the balance tin produced anacceptably malleable metallic coating which resisted cracking when bentor formed. The inventors are of the belief that the uniquecharacteristics of the two-phase metallic tin-zinc system somehowmodifies the rigid characteristics of zinc to allow the tin-zinc coatingto be malleable. In addition to the surprising malleability of thetin-zinc coating, the inventors discovered that the coating providescomparable corrosion resistance to tin-zinc coatings containing largeramounts of tin. Finally, the inventors discovered that the tin-zinccoating containing 65-85 weight percent zinc produced a colored coatingwhich closely matched the gray, earth tone color of weathered terne.Besides terne coatings providing corrosion resistance, terne weathersover time and changes color to a gray, earth tone color. This color hasbecome very popular with consumers; however, the color has been almostimpossible until now to match unless the material was painted. Theinventors have discovered that the high zinc tin-zinc coating changes toa color which very closely resembles the popular grey, earth tone color.The tin-zinc system of application Ser. No. 042,649 does change to agrey color; however, the grey shade is much different from the populargrey, earth tone which is associated with terne coatings.

The tin-zinc metallic coating may also contain small amounts of othermetallic components which can be used to slightly modify the physicalproperties of the metallic coating. The metallic coating may containbismuth and antimony to increase the strength of the metallic coatingand also to inhibit the crystallization of the tin at lowertemperatures. The amount of bismuth in the metallic coating may rangebetween 0-1.7 weight percent and the amount of antimony may rangebetween 0-7.5 weight percent of the coating. Preferably, antimony and/orbismuth are added to the metallic coating in an amount between 0.01-0.5weight percent of the coating. This weight percentage amount issufficient to prevent the tin from crystallizing at low temperatureswhich may result in the metallic coating flaking off the metallicroofing materials. It is believed that the high levels of zinc also helpstabilize the tin within the coating. Antimony and/or bismuth in weightpercentages greater than 0.5% are primarily added to harden and/orstrengthen the metallic coating. Small amounts of other metals, such asiron or copper, may be added to the metallic coating to strengthenand/or increase the pliability of the metallic coating. These othertypes of metals typically constitute very small weight percentageswithin the metallic coating and generally do not exceed more than 2% ofthe metallic coating and preferably are less than 1% of the metalliccoating.

The tin-zinc coating quickly forms a grey, earth tone color whichclosely resembles the color associated with weathered terne coatings.The grey surface is much less reflective than that of coatings of tinand/or non-weathered terne. The-reduced reflective surface of thetin-zinc coating is important in that the coated building materials canbe immediately used on facilities that require materials not to behighly reflective. Prior coatings such as tin and/or terne had to beweathered and/or additionally treated before such coated buildingmaterials could be used on facilities which prohibit the use ofhighly-reflective materials.

The tin-zinc coating can be applied to many types of metals. The twomost popular metals are carbon steel and stainless steel. These twometals are preferably pretreated before coating to clean the materialsurface and remove oxides from the surface so that a strong bond isformed between the material and the tin-zinc coating. Stainless steel isa metal alloy containing iron and chromium. Stainless steel may alsoinclude nickel which can be impregnated within the stainless steeland/or flashed on the stainless steel surface, usually byelectroplating. Carbon steel and other types of metals used asarchitectural material usually do not contain nickel. The inventors havediscovered that if the architectural material is plated with a thinnickel layer prior to coating the material which the tin-zinc coating,the material exhibits improved corrosion resistance in acidicenvironments. If a nickel layer is to be applied, the nickel layer ispreferably plated to the metallic building material by an electrolysisprocess. The thickness of the layer is maintained such that itpreferably is not more than 3 microns (0.0003 in.) thick and preferablyhas a thickness which ranges between 1-3 microns. The bond between thetin-zinc coating and the nickel layer is surprisingly strong and durableand thereby inhibits the tin-zinc coating from flaking especially whenthe building materials are preformed or formed during installation. Theplating of the building materials with the nickel layer is verydesirable when the building materials are used in an environment whichhas high concentrations of fluorine, chlorine and other halogens.Although the tin-zinc coating significantly reduces the corrosiveeffects of halogens on the metallic building materials, the inventorshave found that by placing a thin layer of plated nickel between themetallic building material and the tin-zinc coating, the corrosiveeffects of the halogens are even further reduced.

Examples of the tin-zinc, two-phase metallic coating which haveexhibited the desired characteristics as mentioned above are set forthas follows:

    ______________________________________                                        Alloy                                                                         Ingredients                                                                              A            B       C                                             ______________________________________                                        Tin        15           20      30                                            Antimony   ≦7.5  ≦7.5                                                                           ≦7.5                                   Bismuth    ≦1.7  ≦1.7                                                                           ≦1.7                                   Iron       ≦0.1  ≦0.1                                                                           ≦0.1                                   Copper     ≦2.0  ≦2.0                                                                           ≦2.0                                   Lead       <0.05        <0.05   <0.05                                         Zinc       Bal.         Bal.    Bal.                                          ______________________________________                                    

Generally, the formulations of the tin-zinc metallic coating include inweight percentage amounts; 65-85% zinc, 0-0.5% antimony, 0-0.5% bismuth,15-35% tin and less than 0.01 lead.

The thickness of the tin-zinc coating may be varied depending upon theenvironment in which the architectural materials are to be used. Thetin-zinc coating exhibits superior corrosive-resistant properties ascompared to tin coatings. The metallic coating may be applied in athickness between 0.001-0.05 in. Preferably, the coating thickness isapplied by a hot-dip process and ranges between 0.001-0.002 in. Such acoating thickness has been found to be adequate to prevent and/orsignificantly reduce the corrosion of the metallic architecturalmaterials in virtually all types of environments. Coatings havingthicknesses greater than 0.002 can be used in harsh environments toprovide added corrosion protection.

The tin-zinc coating can be welded with standard lead solders andno-lead solders. Preferably, no-lead solders are used to avoid concernsassociated with the use of lead.

The invention has been described with reference to the preferred andalternate embodiments. Modifications and alterations will becomeapparent to those skilled in the art upon the reading and understandingof the details discussed in the detailed discussion of the inventionprovided for herein. This invention is intended to include all suchmodifications and alterations insofar as they come within the scope ofthe present invention.

Having defined the invention, the following is claimed:
 1. A metal stripunwound from a roll of strip and coated in a continuous hot dip processforming a coating with a highly corrosive-resistant, two phase tin-zinccolored metallic coating, said coating comprising at least 65 weightpercent zinc, at least 15 weight percent tin and at least 0.01 weightpercent metallic stabilizer wherein said stabilizer is a metal selectedfrom the group consisting of bismuth, antimony and mixtures thereof. 2.A coated metal strip as defined in claim 1, wherein said weight percentof said metal stabilizer is up to 9.2 weight percent.
 3. A coated metalstrip as defined in claim 2, wherein said metal additive includes0.01-2.0 weight percent copper.
 4. A coated metal strip as defined inclaim 1, wherein said alloy contains lead.
 5. A coated metal strip asdefined in claim 4, wherein said lead content is less than 0.01 weightpercent.
 6. A coated metal strip as defined in claim 1, wherein saidbase metal strip is coated with a thin nickel layer prior to applyingsaid alloy coating.
 7. A coated metal strip as defined in claim 6,wherein said nickel layer has a thickness up to 3 microns.
 8. A coatedmetal strip as defined in claim 1, wherein said metal strip is stainlesssteel.
 9. A coated metal strip including a base strip of steel or copperwith parallel surfaces both of which are coated with a highlycorrosive-resistant, homogeneous two-phase tin-zinc alloy with zincbeing the primary constituent and tin forming one of said two-phases,said coating being applied by continuously passing the continuous metalstrip through a bath of molten tin-zinc alloy at a speed to deposit ontosaid base strip an impervious two-phase layer of said tin-zinc alloyhaving a uniform thickness on both surfaces in the range of 0.001-0.05inch, said two-phase tin-zinc alloy coating comprising discrete sectionsof zinc in a tin rich matrix, said two-phases being formed byproportioning the zinc and tin to provide a majority by weight zinc andover 15 percent by weight tin with 0.01-11.25 percent by weight of saidcoating alloy being one or more metals additive, which additive does notchange the two-phase characteristic of said coating alloy deposited onthe moving strip wherein said metal additives are selected from thegroup consisting of antimony, bismuth, copper, iron and mixturesthereof.
 10. A coated metal strip as defined in claim 9, wherein saidweight percent of said metal additive is up to 2.0 weight percent.
 11. Acoated metal strip as defined in claim 9, wherein said zinc content is65-85 weight percent and said tin content is 15-35 weight percent.
 12. Acoated metal strip as defined in claim 9, wherein said alloy includes atleast 0.01 weight percent metal stabilizer selected from the groupconsisting of antimony, bismuth and mixtures thereof.
 13. A coated metalstrip as defined in claim 9, wherein said coating thickness is 0.001 to0.002.
 14. A coated metal strip as defined in claim 9, wherein saidalloy contains lead.
 15. A coated metal strip as defined in claim 14,wherein said lead content is less than 0.01 weight percent.
 16. A coatedmetal strip as defined in claim 9, wherein said base metal strip iscoated with a thin nickel layer prior to applying said alloy coating.17. A coated metal strip as defined in claim 16, wherein said nickellayer has a thickness up to 3 microns.
 18. A coated metal strip asdefined in claim 16, wherein said nickel layer is coated by anelectroplating process.
 19. A coated metal strip including a base stripof steel or copper with parallel surfaces both of which are coated witha highly corrosive-resistant, homogeneous two-phase tin-zinc alloy withzinc being the majority constituent and tin forming at least 15 weightpercent of said two-phases, said coating being applied by continuouslypassing the continuous metal strip through a bath of molten tin-zincalloy at a speed to deposit onto said base strip an impervious two-phaselayer of said tin-zinc alloy having a uniform thickness on both surfacesin the range of 0.001-0.05 inch, said two-phase tin-zinc alloy coatingcomprising a majority of zinc and formed by discrete sections of zinc ina tin rich matrix, and wherein said base strip is plated with a thinlayer of metal prior to applying said two-phase metallic coating,wherein said two-phase coating alloy includes 0.01-2.0 weight percentmetal additive selected from the group consisting of antimony, bismuth,copper, iron and mixtures thereof.
 20. A coated steel strip as definedin claim 19, wherein said metal layer is nickel.
 21. A coated metalstrip as defined in claim 19, wherein said metal layer thickness is upto 3 microns.
 22. A coated metal strip as defined in claim 19, whereinsaid metal layer is electroplated onto said metal strip.
 23. A coatedmetal strip as defined in claim 19, wherein said two-phase coating alloyincludes lead.
 24. A coated metal strip as defined in claim 19, whereinsaid steel is stainless steel.
 25. A coated metal strip as defined inclaim 19, wherein said zinc content is 65-85 weight percent and said tincontent is 15-35 weight percent.
 26. A coated metal strip as defined inclaim 19, wherein said metal additive includes 0.01-2.0 weight percentcopper.
 27. A coated metal strip including a base strip of stainlesssteel with parallel surfaces both of Which are coated with a highlycorrosive-resistant, homogeneous two-phase tin-zinc alloy, said coatingbeing applied by continuously passing the continuous metal strip througha bath of molten tin-zinc alloy at a speed to deposit onto said basestrip an impervious two-phase layer of said tin-zinc alloy having auniform thickness on both surfaces in the range of 0.001-0.05 inch, saidtwo-phase tin-zinc alloy coating comprising a majority of zinc and atleast 15 weight percent tin and formed of discrete sections of zinc in atin matrix, wherein said two-phase coating alloy includes 0.01-2.0weight percent metal additive selected from the group consisting ofantimony, bismuth, cooper iron and mixtures thereof.
 28. A coated metalstrip as defined in claim 27, wherein said strip includes chromium. 29.A coated metal strip as defined in claim 27, wherein said strip includesnickel.
 30. A coated metal strip as defined in claim 28, wherein saidstrip includes nickel.
 31. A coated material strip including a basestrip of stainless steel with parallel surfaces both of which are coatedwith a highly corrosive-resistant, homogeneous two-phase tin-zinc alloy,said coating being applied by continuously passing the continuous metalstrip through a bath of molten tin-zinc alloy at a speed to deposit ontosaid base strip an impervious two-phase layer of said tin-zinc alloyhaving a uniform thickness on both surfaces in the range of 0.001-0.05inch, said two-phase tin-zinc alloy coating comprising a majority ofzinc and at least 15 weight percent tin and formed of discrete sectionsof zinc in a tin matrix, wherein said alloy includes 0.01-2.0 weightpercent cooper.